We say:

These kind of trousers are quite difficult to find for young people, they are properly waterproof but they are pretty much a standard pair of outdoor trousers, so you can wear them on a hike and not have to think about bring waterproof over-trousers too.

Trousers for kids that can be worn all day but are also fully waterproof. Ideal for hiking, wear them against the skin or layer over thermals. 

• Technical waterproof trousers
• Waterproofing WP - 8,000 mmHg
• Breathable WVP -  5000 g/m2/24h
• Fully taped seams
• Reinforced knees and backside
• Zip hand-warmer and thigh pockets
• Velcro adjustment at base of trousers
  
• Mesh lined upper section, smooth lining in lower section.
• Contoured shaped knees for fit and comfort
  
• Waistband with belt loops and elastic adjustment
• Width adjustment at ankles 
• Ankle zips
• Breathable and quick drying